The present invention relates to an atmospheric pressure ionization mass spectrometer system, in which the sample solution is introduced and ionized under atmospheric pressure and the resultant ions are introduced into the high-vacuum mass spectrometer for mass analysis.
Recently, a liquid chromatograph directly coupled to an atmospheric pressure ionization mass spectrometer system (LC/MS) has been widely used for high sensitivity analysis of trace amounts of valuable or harmful materials in many organic compounds which exist in environments, food or organisms. This apparatus couples a liquid chromatograph (LC) of separating means and an atmospheric pressure ionization mass spectrometer system (API-MS) of high sensitive qualitative quantification means. LC/MS has been widely used in areas such as pharmacy, medicine, chemistry, and environmental science.
FIG. 7 schematically shows a general LC/MS. LC1 separates the sample solution into constituents. Separated constituents and mobile phase solvent pass through together a capillary tube 2 into an atmospheric pressure ion source 4. After arriving at a spray probe 3 of the atmospheric pressure ion source 4, the sample solution is sprayed into the atmosphere as charged fine droplets. The spraying is caused by high voltage applied to the probe 3 from a high voltage supply 5. The fine droplets travel in the atmospheric pressure ion source 4 to collide with the atmospheric molecules and become finer. Finally, the ions are emitted into the atmosphere. This is how the Electro-spray ionization (ESI) operates. The generated ions 6 move into the vacuum chamber 12 through the fine aperture or fine tube 8 on the vacuum wall of the mass spectrometer. The ions 6 then move to the vacuum chambers 15, 19 and into the mass spectrometer 17, which can mass analyze the ions 6 to provide mass spectrum.
In the atmospheric pressure ionization mass spectrometer system, are very important the fine aperture or fine tube between the atmospheric pressure ion source and the mass spectrometer of vacuum system. The atmospheric pressure ionization mass spectrometer system carries out the ionization under atmospheric pressure (105 Pa). The mass spectrometer needs, however, to work in a much lower pressure (10−3 Pa or less). Thus, the ions must move into the mass spectrometer against a pressure difference of eight orders of magnitude. Usually, large vacuum pumps 20, 21, 22 are used to much of the gas introduced with the ions. However, there is generally a limit to the size and number of vacuum chambers in terms of economy and structure. Thus, throttle has been used to control the gas flow from the atmospheric pressure ion source to the mass spectrometer. The throttles is the fine aperture or fine tube on the partition wall between the atmospheric pressure ion source and the mass spectrometer. U.S. Pat. Nos. 4,121,099, 4,137,750, 4,144,451, and 4,935,624 disclose an atmospheric pressure ionization mass spectrometer system with a fine aperture. U.S. Pat. Nos. 4,542,293, 5,245,186 disclose an atmospheric pressure ionization mass spectrometer system with a fine tube.